The purpose of this study is to investigate whether radiotherapy given as three large doses over a period of two weeks (hypofractionated radiotherapy) is more effective than standard radiotherapy for patients with non-small cell lung cancer that has not spread beyond the lung. Although surgery is the most effective treatment for early lung cancer, many patients are not fit enough for an operation. The alternative treatment to surgery is standard radiotherapy which is normally 'fractionated' that is, given as a number of small doses over a period of weeks. Experience has shown that many small treatments are safer than using a few large doses (hypofractionation) because there is less risk of damage to normal tissues.